1. Field of the Invention
This invention relates to an apparatus for filtration of material such as suspended solids, from a liquid effluent. The apparatus has particular utility as a filter, particularly as a tertiary filter, in a wastewater treatment method and is particularly useful in reducing the last few ppm (parts per million) of solids in a previously treated wastewater effluent.
2. Background of the Invention
In my previous application, I disclosed the use of felt or pile fabric as a filter medium for a tertiary filter in a wastewater treatment process and apparatus. The use of pile fabric has become of particular interest as a filter media. A pile fabric of particular interest in this invention typically has a long-napped filter cloth or pile comprised of a plurality of fiber bundles of up to about 15 mm in length secured to a woven fiber backing. The fiber bundles, when in use, matt down to form the filter surface. Such a material has good filtering properties, but when used as a filter media, can become occluded or clogged with solid particles removed from a suspension of particles from an effluent such that the particles are retained within, and between, the fiber bundles of the filter media. It has been previously proposed to backwash a filter media comprising fiber bundles with a suction head which exerts a mechanical pressure on the leading edge of the head with an abrupt release of pressure to cause the fiber bundles to straighten abruptly within a suction slit in the suction head; See, U.S. Pat. No. 6,103,132, the entire disclose of which is herein incorporated by reference.
However, such a process has various drawbacks, including low efficiency of filtering as the suction applied within the slit does not compensate for the varying surface areas of the filter to be backwashed. Furthermore, wear of the filter media by the impingement of the leading (and trailing) edge of the suction head against the filter media may also occur. In addition to wear of the fiber bundles comprising the pile, the mechanical pressure tends to pull the fiber bundles away from the woven fiber backing enlarging the apertures in the backing further resulting in loss of filtering efficiency. Still further, the filter media backing is pulled away from its supporting grid of structural material tending to stretch and misshape the filter media backing resulting in wrinkles in the filter media further impeding the movement of the suction head over the filter media. The filter media, when also subjected to mechanical pressure by the trailing edge of the suction head, also contributes to wear of the filter media. Continued use of the suction head under such conditions degrades the filter media and can pull out fibers or parts of the fiber bundles of the filter media and can even rupture the woven fabric backing resulting in premature failure of the filter media. Of course, upon failure of the filter media, the entire filtering process is disrupted, causing the filtering process to be interrupted and the filter tank in which the filter media of the prior art is contained needs to be drained, and the filter media replaced.
Moreover, the arrangement of the pile filter media in the aforementioned U.S. Pat. No. 6,103,132 is mounted on a rotating shaft, with seals on the shaft about which the filter rotates. Not only do the seals leak resulting in dimunition of filter efficiency, but when the filter media fails, through either excessive wear of the fiber bundles, tear out of the fiber bundles from the fabric backing, holes in the fabric backing or, otherwise, the apparatus must be shut down, the tank in which the rotating filter is located must be drained, and the filter wheel disassembled to replace the filter media. Thus, the entire tank is taken out of commission. Furthermore, in the prior art, if one wished to increase capacity of filtering, the entire filter apparatus, including tank, and rotating filter must be duplicated when additional capacity is desired.
The invention avoids all the drawbacks of the prior art filter disclosed in U.S. Pat. No. 6,103,132.